CVE-2023-52993 is a vulnerability identified in the Linux kernel's handling of legacy Programmable Interrupt Controller (PIC) interrupts on x86 architectures, specifically related to the i8259 interrupt controller. The issue arises from improper marking of legacy PIC interrupts with the IRQ_LEVEL flag, which indicates level-triggered interrupts. The vulnerability manifests when a spurious Advanced Programmable Interrupt Controller (APIC) interrupt on the IRQ0 vector is erroneously resent in software within a soft interrupt (tasklet) context. In this context, the function get_irq_regs() returns NULL, leading to a NULL pointer dereference in the periodic tick code. This causes instability such that after triggering a crash, the subsequent crash-kernel fails to boot approximately 50% of the time. The root cause is that legacy PIC interrupts are level-triggered and should not be resent in software, but the IRQ_LEVEL flag was never set for these interrupts, causing the kernel core code to misinterpret their trigger type. The fix involves ensuring that the IRQ_LEVEL flag is set correctly when legacy PIC interrupts are initialized, preventing the spurious resend and subsequent NULL pointer dereference. This vulnerability affects Linux kernel versions identified by the commit hash a4633adcdbc15ac51afcd0e1395de58cee27cf92 and likely related versions prior to the patch. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations relying on Linux-based systems, especially those running on x86 hardware with legacy PIC interrupt configurations, this vulnerability could lead to system instability and denial of service conditions. The inability of the crash-kernel to boot reliably after a system crash could hinder recovery processes, impacting availability of critical services. This is particularly concerning for infrastructure that depends on high availability and rapid recovery, such as telecommunications, financial services, and industrial control systems. While the vulnerability does not appear to allow privilege escalation or direct code execution, the resulting kernel crashes and boot failures can cause significant operational disruption. Systems running older or unpatched Linux kernels are at risk, and organizations with automated crash recovery mechanisms relying on crash-kernels may experience degraded resilience. Since no known exploits exist yet, the immediate risk is moderate, but the potential for exploitation to cause denial of service warrants prompt attention.

European organizations should prioritize updating their Linux kernels to versions that include the patch addressing CVE-2023-52993. Specifically, ensure that the kernel version includes the fix that sets the IRQ_LEVEL flag correctly for legacy PIC interrupts. For environments where immediate patching is not feasible, consider disabling legacy PIC interrupt support if hardware and workload allow, or configure system monitoring to detect frequent kernel crashes or crash-kernel boot failures. Additionally, review and test crash recovery procedures to verify that crash-kernels boot reliably post-update. System administrators should audit their kernel configurations and interrupt handling settings to confirm compliance with best practices for interrupt management. Engaging with Linux distribution vendors for timely security updates and applying them as part of regular patch management cycles is critical. Finally, maintain robust backup and disaster recovery plans to mitigate potential downtime caused by this vulnerability.